The present invention relates to a die for coextrusion of two doughs into a dough log with a cross section that includes a complex center shape, such as of an animal, made from a first identifiable dough, surrounded by a second dough to form the dough log. The dough is extruded through dies and then moves into a sizing housing that changes smoothly in cross section from a constant size chamber to the outlet opening to maintain a sharp definition of the center cross section dough relative to the outer dough.
In the prior art, two food materials such as cookie dough have been extruded simultaneously, to form an interior core of a selected shape. Machines for coextrusion are made by Rheon Automatic Machinory Co., Ltd., Utsonomiya Japan and by Bepex GMBH of Leingarten, Germany. Both companies have coextrusion die heads that are suitable for certain applications, including making candy, and also for forming cookie dough, but the dies used do not provide satisfactory definition between the interior cross sectional shape and the outer surrounding material, such as a cookie dough, when the dough is extruded through the dies. As the shape of the internal cross section is made intricate the definition drops significantly.
The Rheon extruder has dies that control flow by restricting the flow passages to small holes and slots, and the flow is shaped by filling a cavity of the desired center cross sectional shape with a first dough around which an outer dough is extruded. This system has limitations as to its capacity because of the size of the restriction holes in the die. In high production of cookie doughs for example, the small holes are not economical.
The Bepex extruder uses an open die that is designed to account for flow expansion of the dough after passing through the die, and a housing cavity forms the center shape downstream of the die opening. The dies are developed by trial and error and are dependent on the rheology of the dough remaining constant to work reliably. In extruding large quantities of cookie dough, the flow properties of the dough cannot be controlled sufficiently accurately to insure maintaining sharp definition between the center cross section dough and the outer surrounding dough. Relatively sharp corners and small fillets will lose definition. Thus, a problem remains with the use of dies that have adequate flow properties, because they do not provide the desired product shape definition in the extruded dough log.